Steel structural members have been used in the construction of mattress foundations, such as disclosed in U.S. Pat. Nos. 4,129,908, and 4,218,790 as for example laterally arranged cross members attached at ends to a rectangular frame to provide increased strength and rigidity. An array of steel members or spans may be perpendicularly intersected by a longitudinally disposed center beam passing underneath the spans and also attached to the wooden rectangular frame. Steel spans also serve to support foundation springs which, as disclosed for example in U.S. Pat. Nos. 3,971,081 and 4,779,292 are inserted into cross-sectional slots formed in opposing walls of the steel spans.
Such steel spans have been formed in generally U-shaped cross-sectional configurations having opposed walls in order to attain desired strength and flexure characteristics, and to enable formation of the cross-sectional slots in opposed walls into which the foundation springs are inserted. However, improvements have not been made to steel span designs which optimize strength and flexure characteristics and which improve ease and accuracy of production and quality control. To produce steel spans with progressive roller dies in a U-shaped cross-section with a rounded portion connecting the vertical walls have been unsuccessful due to the tendency of the span to roll or scew off of the longitudinal centerline.